The Chinese meaning of "你是个天才" is to praise someone for having high natural endowments or intelligence, indicating a high degree of recognition of their wisdom and abilities.but sometimes people might use it to sarcasm someone for doing something particularly strange.

This phrase is normally used when you are speaking to your friends or juniors. If they have done a great job, “你是个天才” is a positive appraisal. If they have done something wrong, and you are angry, you may say “你(真)是个天才!” to deliver you anger.

You are a genius. This is a compliment, but it is usually a bit exaggerated. It expresses extreme admiration and praise for you, such as you have accomplished something, or some performance is very outstanding. There are usually two situations: one is true admiration, and the other is pampering praise (such as a mother to her son)

If you do well in the exam, I would say: you are a genius. you are smart 👍🏻 If you do something wrong, 你是个天才 it's means opposite meaning.